JPS6334893B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a propylene-based resin foam molded product that is foam-molded in a substantially non-crosslinked state and a method for producing the same, and more specifically, the present invention relates to a propylene-based resin foam molded product that is foam-molded in a substantially non-crosslinked state, and more specifically, to a method that fully utilizes the properties of propylene resin (e.g., heat resistance, rigidity, oil resistance, etc.). The present invention relates to an improved foamed molded article made of expanded propylene resin particles, which has a cushioning property with repeated durability in a state where the article is held in place, and a method for manufacturing the same. With the development of in-mold molding methods for polyethylene foam particles, expanded propylene resin particles and methods for producing molded articles made from the particles have been introduced in many documents. For example, the
Publication No. 22951, Japanese Patent Publication No. 53-33996, and Japanese Patent Application Publication No.
Publication No. 56-46735 basically describes the steps of (a) crosslinking a resin and incorporating a volatile foaming agent therein to form foamable resin particles, and (b) expanding the foamable resin particles to form foamed particles. (c) A step of imparting foaming ability to the foamed particles to be exhibited in the mold (increasing the internal pressure of the particles, compressing the particles to reduce their volume), (d) utilizing the foaming ability. Step of foaming (expanding) and heat-sealing the foamed particles to each other in a mold to form a foamed molded product according to the mold; (e) Taking out the foamed molded product while cooling; A method for in-mold molding of expanded particles of crosslinked polyolefin (actually crosslinked polyethylene) comprising a combination of (e) is described. These are generally produced as molded articles with an average cell diameter of 0.5 to 0.05 mm and a high closed cell ratio, with a density in the range of 0.015 to 0.1 g/cm ³ depending on the intended use. Therefore, propylene resins, which are a subordinate concept of polyolefins, are introduced as if they could be used to make excellent foam molded products if applied as they are. On the other hand, for example, Japanese Patent Publication No. 49-2183, Japanese Patent Publication No. 56
JP-A-1344 discloses a method for producing expanded propylene resin particles in which the steps (a) and (b) above are performed in a non-crosslinked state. Therefore, if the above two methods are combined, an in-mold molding method using non-crosslinked propylene resin foam particles can be completed very easily according to the literature. However, in reality, it is not so simple, and a foam molded product that can be put to practical use cannot be obtained. One of the proofs is that although the completion of substantially non-crosslinked propylene resin foam molded products is often reported in newspapers and other publications, the reality is that they are being developed into various shapes for practical use. When transferring to the production process, there were many problems such as communication of bubbles, unevenness of bubbles, sink marks, poor fusion, etc., and the characteristics were as per the design values shown in catalogs etc., especially the characteristics that took advantage of the characteristics of propylene resin. Because it is not possible to stably supply molded bodies that meet these requirements, the current situation is that they still cannot be listed as commercially available foams. The reason for this is that propylene resin has a higher degree of crystallinity and a higher melting point than, for example, polyethylene, and its fluid viscoelastic properties during melting have a greater temperature dependence. It is necessary to maintain sufficient foaming ability up to the temperature range, to control the temperature within a very narrow temperature range suitable for foaming, and to handle the crystallization heat generated when the molten resin solidifies. Furthermore, this can be realized using an in-mold molding method in which the particles filled in the mold are directly heated with steam or the like to foam, and then cooled with water or the like from the outside to form a molded product. For example, if you raise the water vapor temperature because the internal temperature is insufficient, particles on the surface will begin to fuse together, blocking the flow of water vapor.
This is because the troublesome phenomenon of an insufficient internal temperature is added, making the harmonization even more difficult. On the other hand, the means for modifying the propylene resin mentioned above include
Methods of crosslinking and methods of copolymerizing and mixing other monomers and other polymers have been known for a long time. If the content of the above-mentioned monomers and polymers is sufficient to increase the quality of the melt-foamed material, the resulting foam will lose its properties as a propylene-based resin. There are drawbacks that do not lead to each good in applicability, and a middle ground cannot be found. Therefore, at present, we are relying on a modification method that involves crosslinking, even though we are aware that it is uneconomical. In the technique disclosed in Publication No. 46-38716, a specific propylene-ethylene copolymer is cross-linked, and when this is made into a foam, a chemical blowing agent with low volatility is used (see Examples). ). The present invention has been made in view of the current situation, and its first purpose is to provide a substantially non-crosslinked propylene resin foam molded product with improved thermal stability (thermal dimensional stability), oil resistance, rigidity, etc. The purpose is to provide a foam molded product that has the characteristics of a propylene resin and also has a high level of cushioning properties and repeated durability.The second purpose is to make the foam for the above purpose more economical. An object of the present invention is to provide a foam molding method using foamed propylene resin particles that can be stably supplied. The first object of the present invention is to provide a foam molded article constituted by a large number of propylene resin foam particles having a fine cell structure, which are fused and aggregated with the surfaces of adjacent particles in contact with each other, (a) The propylene resin is a propylene-ethylene random copolymer with a propylene component of 90% by weight or more and an ethylene component of 10% by weight or less,
Random coefficient (R) is 0.7 or less, stereoregularity of propylene segment () is less than 40%, 5Kg
The copolymer has a softening point under load of approximately 50 to 35°C, (b) the resin foam is substantially non-crosslinked, and (c) the resin foam formed by the above fusion aggregation By employing a foam molded product made of polypropylene resin foam particles, the fused film is about 8 times or more thicker than the cell membrane inside the particles. , and the second object of the present invention is to produce propylene containing 90% by weight or more of propylene component and 10% by weight or less of ethylene component.
An ethylene random copolymer with a random coefficient (R) of 0.7 or less, a stereoregularity of propylene ^segments ( A volatile organic blowing agent with a boiling point of -50 to 110°C is added to the copolymer shown to form expandable resin particles, and then the blowing agent present on the surface of the expandable resin particles is preferentially volatilized. After this, the entire particle is foamed to form a foamed particle having a thick skin, and then the foamed particle is given foaming ability and is heated and foamed in a non-crosslinked state in a mold, so that the particles bond with each other. The surfaces are fused to form an integrated molded body, and the fused film produced by the fusion is approximately 8 times or more larger than the cell membrane that constitutes the particles inside the molded body. Both of these can be easily achieved by employing a method for producing a molded body made of expanded propylene resin particles. Hereinafter, the contents of the present invention will be explained in detail using drawings and the like, starting with the second invention (manufacturing method). However, this explanation is merely a convenient means for deepening the understanding of the content of the present invention, and this explanation explains how the first invention (molded article) can be understood from the second invention.
It is not subject to the restrictions of the invention. This is because the explanation of what makes in-mold foaming of non-crosslinked propylene resin possible in the present invention and why the molded product has come to have various properties not previously recognized is beyond the scope of this book. It would be better to explain in order the structure of the foamed particles brought about by the production method of the invention, the role played by the particles in the method, and the structure and function that it has when it becomes a foamed molded product. This is because I thought that understanding these relationships would lead to a true understanding of the technical idea of the present invention. On the other hand, once the technical idea of the present invention is deeply understood, it will be easier to accomplish the present invention in other ways. FIG. 1 is a representative photomicrograph of the foamed particles used in the present invention, and FIG. 2 is a representative photomicrograph of the foamed particles used for comparison (conventional). In addition, the comparison between Figures 1 and 2 shows that "the foaming agent present on the surface of the foamable resin particles is preferentially volatilized, and then the entire particles are foamed", which corresponds to the second invention part. Figure 1, which satisfies the requirements, and Figure 2, which uses the same type of resin but does not go through the above requirements, especially the step of "preferentially volatilizing the blowing agent present on the surface of the particles", using a normal foam particle manufacturing method. It also means the comparison between This difference is that in FIG. 1, an independent cell structure with finer cells is formed compared to that in FIG. 2, and compared to the average cell film 2 inside. The fact that a thick skin portion 1 is formed can be directly observed objectively. That is, the thick skin part in FIG. 1 is considered to be formed by slight foaming failure in the skin part caused by the volatile organic foaming agent that was preferentially volatilized. This thick skin portion first imparts expansion ability (this is called self-expansion ability) to the foamed particles themselves. Self-expansion ability can be confirmed by leaving the foamed particles in the air for several days to fully volatilize the foaming agent inside them, then heating them with steam at 143°C for 5 seconds, and heating them at room temperature at 90°C. After leaving it for 15 hours, further heat it to 25℃.
The volume of the particles left for 24 hours is divided by the volume of the original expanded particles. On the other hand, the one shown in Fig. 2 shows a value less than 1.1 times at most. Next, in the second invention, the foamed particles are further "imbued with foaming ability" in order to more completely foam within the mold. This foaming ability is added to the above-mentioned self-expansion ability, and specifically, the internal pressure of the foamed particles is adjusted to a uniform value within the range of 0.5 to 3 Kg/cm ² (gauge pressure). Fill with inorganic gas (foaming agent gas) such as air, or
This can be achieved by compressing the expanded particles to a bulk volume of 95 to 50% of the original bulk volume, or by performing one or a combination of both operations. However, in the present invention, it is not necessary to choose a condition for giving a high value, and at most
A range of 0.5 to 2 Kg/cm ² (gauge pressure) and 95 to 70% is sufficient. At this time, the thick skin part, in cooperation with the fine cells held inside, controls the function of maintaining the applied internal pressure for a long time or the function of increasing the repulsion force per unit compression generated by the compression. . In addition, this effect is caused by factors such as temporal fluctuations that the foamed particles undergo during the process of heating and expansion in the mold, or temperature fluctuations caused by the difficulty of uniform heating in the mold. This prevents the foaming performance from changing and becoming locally insufficient, and also facilitates the management of expandable foam particles and the setting of molding conditions. Regarding foaming in the mold as mentioned above,
In the method of the present invention, which uses foamed particles that have been modified multiple times, simply by ``heating and foaming them in a non-crosslinked state in a mold'', it is possible to ``fuse the surfaces of the particles to create an integrated mold.'' This results in a non-crosslinked molded product with perfect internal fusion, no marks, and a beautiful surface, something that no one has ever been able to achieve before. The reason for this is that the thick skin of the foamed particles described above works in conjunction with the thermal properties of the specific resin of the present invention, which will be described later. This allows for a relative range of molding conditions, such as the availability of high-temperature (i.e. high-pressure) water vapor, which previously could not be employed, and this also allows the mold to pass through the interparticle spaces and In addition to increasing the temperature-raising function of the steam that heats even the foamed particles located inside, this makes it possible to uniformly heat the inside of the mold in an extremely short period of time. In addition, the foamed particles heated in the mold are held in a state where they can easily exhibit the foaming ability imparted as described above,
Moreover, it has self-expansion ability, which allows it to foam in a stepwise manner that is not seen before, filling every nook and cranny between particles with its generous foaming power, completing dense interparticle fusion. It is presumed that Figure 3 shows the expanded particles according to the present invention (Figure 1),
FIG. 4 is a microscopic photograph illustrating a cross section of a molded product obtained by molding the expanded particles of comparison (FIG. 2). In comparing FIGS. 3 and 4, the one shown in FIG. 3 (present invention) has a common feature of the present invention, namely, "the fused film 4 produced by fusion aggregation is inside the particles. It can be seen directly that the film thickness is approximately 8 times or more thicker than the cell film 3, and satisfies the requirements for forming a molded body. Needless to say, this fused film 4 is formed by the thick skin part 1 of the foamed particles referred to in the present application being deformed and fused by expansion. However, as mentioned above, the thick skin part of the foamed particles is effective because the method of the present invention adopts the operation of "preferentially volatilizing the blowing agent present on the surface part of the foamable resin particles". However, not all propylene resins can be subjected to in-mold foam molding. According to the findings of the present inventors,
Rather, most of these are those that cause uneven foaming or insufficient foaming, those that are difficult to form foamed particles with a thick skin, those that cannot be subjected to in-mold foam molding in a non-crosslinked state, and those that Even if the product can be made into a foamed molded product, there will be causes of failure, such as those that do not exhibit the expected properties, so care must be taken when selecting the resin. The propylene resin used in the present invention was finally extracted through repeated modifications and careful selection of propylene resins. The outline of the process is that, for example, with propylene homopolymers and copolymers with other monomers, it is difficult to form a thick skin, and when foaming without crosslinking, foaming spots occur. However, there is a drawback that it is difficult to obtain a foam of the desired high quality. Furthermore, even when using the same propylene-ethylene copolymer, it is difficult to uniformly foam the block copolymer. On the other hand, even in random copolymers, when the ethylene component is as high as 10% by weight, there is a marked tendency for ethylene to copolymerize in blocks, and the softening temperature of the copolymer decreases, resulting in propylene-based copolymerization. This is undesirable because it loses its properties as a coalesce, and conversely, if the amount is less than 2% by weight, no modification effect can be obtained. In addition, even when using a propylene ethylene random copolymer with an ethylene component within the range of the present invention, one with a random degree (R) exceeding 0.7 (that is, one close to a block copolymer) is not suitable for homogeneous foaming. is difficult to carry out, and the foaming ratio cannot be increased. Even if the degree of randomness (R) is 0.7 or less, in the present invention, it is necessary to select one with low stereoregularity (). That is, if the stereoregularity ( ) is large, for example, 40% or more, it is difficult to make it into a foam in a non-crosslinked state and utilize the characteristics of the resin in the foam. In addition, in the present invention, the Vikatsu softening point at a load of 5 kg is
A temperature range of 50 to 35°C is selected. This necessity is to adjust the delicate balance of the flow deformation of the resin that occurs during heat foaming when foamed particles with a thick skin are molded in a mold. In this case, the flow deformation of the resin on the inner surface of the mold progresses easily, and on the other hand, if the temperature exceeds 50℃, the flow deformation is slow overall, leaving depressions or fusion between particles on the surface of the mold. Defects are likely to occur,
In either case, the applicable molding temperature range is narrowed, and a molded article of good quality cannot be obtained. The propylene-ethylene random copolymer carefully selected in this way has a melting point of approximately 140 to 120°C, which facilitates the formation of a thick skin when forming foamed particles, and This makes it possible to set the molding conditions for a molded product that is foamed without crosslinking and has a smooth surface that is well fused even to the inside, with unprecedented homogeneous foaming. However, in reality, the random coefficient (R) is 0.7,
As the stereoregularity () increases to 40%, uniform foaming tends to become more difficult, so for products with a large stereoregularity () of 40%, crosslinking, such as surface crosslinking, which accounts for several percent of the total was applied. Better quality foam can be obtained. In order to stably supply a completely non-crosslinked product, it is preferable to carefully select a resin with a random coefficient (R) of 0.4 and a stereoregularity () of 15% or less from the above resin range. . Also, if the skin part of the foamed particles becomes too thick, the particles may crack during foaming, foaming defects may occur, or the molded product may have abnormal hardness. It is advantageous to form a fused film that is about 15 times larger than the cell film inside the expanded particles. Next, the first invention (molded body) of the present invention will be explained. The propylene ethylene random copolymer specified in the first invention has, in addition to the above-mentioned advantages in the manufacturing method, when formed into a foam, it has, for example, oil resistance and heat resistance (dimensional stability over time). Excellent. This advantage is that the essential properties of the propylene resin can be utilized as they are in the copolymer foam. In addition, the non-crosslinking feature not only makes the foam more economical due to the simplification of the manufacturing process, but also makes it possible to reuse the foam as a propylene resin, reducing pollution problems caused by disposal and saving resources. It has the advantage of contributing to countermeasures for the problem. Next, as a characteristic advantage of the first invention, dynamic buffering properties, compression set resistance, repeated compression set resistance, degree of particle fusion of the molded body, etc. are all at a high level. be. For example, when the molded article of the present invention is applied to a buffer molded container that is used repeatedly as a returnable container, it can maintain sufficient buffering capacity and can be made into a robust container that is less likely to break. have This advantage is due to the fact that in addition to selecting the specific copolymer of the present invention, propylene resins were conventionally considered to be too rigid and easily formed into brittle foams. As shown in Fig. 3, it is foamed into a relatively homogeneous fine cell structure, on which a large number of thick fused films 3 are arranged almost three-dimensionally regularly inside the molded body, and it is strong. It is presumed that this was possible due to the close coupling between the two. By the way, Figure 5 A and B are diagrams showing the buffer characteristics.
A shows the relationship between the static stress and the maximum deceleration G, and B shows the relationship between the instantaneous maximum strain in comparison with commercially available foams. Other characteristics of the molded product of the present invention shown in FIG. 5 are shown in Example 4, and it is well proven that it is a high quality foam. In the present invention (method), after preferentially volatilizing the blowing agent present on the surface of the expandable resin particles,
A typical method for "foaming the entire particle" is to place expandable resin particles containing a predetermined amount of a volatile organic blowing agent in a foaming pot and blow a heat medium (e.g., steam) into the foam to raise the temperature. Foam at a warm temperature. At this time, normally, in order to increase the foaming efficiency, one tries to shorten the heating time to the foaming temperature, but in this method, on the contrary, the temperature is raised to the foaming temperature. It is practical to adopt a method in which the foaming agent present on the surface of the particles is preferentially volatilized by increasing the time, and then the entire particle is foamed at the foaming temperature reached. At this time, the foaming temperature and heating time should be set appropriately depending on the foaming agent used.
If the heating time is too long, the blowing agent inside the particles will also evaporate, resulting in poor foaming. Therefore, it is necessary to conduct preliminary experiments in advance to determine the conditions that are suitable for the blowing pot and blowing agent. It is necessary to find out. In short, in this method, the blowing agent on the surface of the expandable resin particles, which is closer to the foaming agent-containing state, is removed at a temperature somewhat lower than the foaming temperature or at a pressure somewhat lower than the equilibrium pressure, prior to the foaming of the entire particle. Since it is completed by volatilization under certain conditions, it can be reproduced in various ways, whether in gas or liquid. In describing the manufacturing method of the second invention, a method for manufacturing expandable particles, a method for foaming expanded particles, a method for imparting foaming ability to occur in a mold, a method for filling into a mold and molding in a mold, and a method for measuring internal pressure. For example, the basic contents are described in the publications cited in the main text, and these are well known as the manufacturing process conditions for olefins and crosslinked olefins. Since it is only necessary to adopt a method suitable for the process, its description has been omitted. The propylene resin used in the present invention uses a halogenated titanium compound represented by the general formula TiXn (where X represents chlorine, bromine or iodine, and n is 2 or 3) as a catalyst as the first component, and Metals of Group A or Periodic Table A to A
The second component is an organometallic compound of group metal, and optionally, the third component is an organic compound containing electron-donating N, P, O, S, etc. or an inorganic salt such as an alkali metal halide or an alkali metal oxyacid. Random copolymerization with the desired ethylene content can be achieved by continuously supplying ethylene and propylene at a fixed ratio and adjusting the ethylene concentration in the gas phase. It is produced by polymerizing at 40 to 90°C so that it coalesces. The catalyst, polymerization temperature, polymerization medium, polymerization method, product post-treatment method, etc. to be used are particularly limited as long as a copolymer with appropriate randomness, isotacticity, and softening temperature can be obtained for use in the present invention. Not done. The random coefficient (R) referred to in the present invention is a calculated value based on the measurement of infrared absorption spectrum, and is a resin film made by carefully pressing it to a uniform thickness in the range of 250 to 300μ using the test piece preparation method described in JIS K6758. For infrared spectrometers (e.g. PerkinElmer
521 type), and adjusted the scanning speed so that the waveforms of the absorption at 722 cm ^-1 corresponding to the block-copolymerized ethylene component and the absorption at 733 cm ^-1 of ethylene were accurately measured. Measure at room temperature of 25℃, calculate the transmittance using the baseline method,
Calculate the absorbance at 722 cm ^-1 (A ₇₂₂ ) and the absorbance at 733 cm ^-1 (A ₇₃₃ ), and calculate the ratio R, (R=
A ₇₂₂ /A ₇₃₃ ) is the random coefficient. The principle of the calculation formula is A=-LogI/Io, so ( _A733 = _-LogI733 / _Io733 ), ( _A722 = _-LogI722 / _Io722 ). The stereoregularity ( ) of the propylene segment in the present invention is approximately
Form into a sheet with a thickness of 100μ, and fold this sheet into 3
Samples were cut into small pieces of mm square. Molding condition,
Post-treatment conditions were conducted in accordance with the test piece preparation method described in JIS K6758. The accurately weighed sample was extracted using a Kumagawa extractor at the boiling point of n-heptane for 8 hours, dried in a vacuum dryer at 80°C under a reduced pressure of 2 mmHg for 8 hours, and the residue was accurately weighed. The ratio to the original weight was expressed as (%), and this was defined as the stereoregularity () of the propylene segment. The Vikatsu softening point in the present invention is based on ASTM D1525.
This is the value when measured under the condition of 5 kg load according to . The evaluation method and evaluation criteria for the characteristics evaluated in the present invention will be described below. Measurement of the thickness of the skin part of foamed particles and the bubble film inside the particles 20 pieces of 20 roughly spherical foamed particle samples were cut at the center cross section of each sample.
Regarding the cut surface of ke, 0.25R from the center of the surface,
Electron micrographs (450x) of the film thickness of the bubbles and skin at positions of 0.75R and 0.9R (R is the average radius of the cut surface) were taken, and the length of the cut bubble film was 0.34D (D
2, 18, and 26 membrane cross-sectional areas with a diameter greater than or equal to the average cell diameter were randomly selected from 2, 18, and 26 locations within each particle, and 32 locations from the epidermis, and the film thickness at the center of the cut surface of each bubble membrane was measured. For the cell membrane within the foamed particles, the thickness was determined by Mitsuki's average value, and for the skin portion, the arithmetic average value was determined as the thickness. The skin thickness ratio was determined by calculating the average skin thickness/average bubble film thickness. Foamed particle fused film thickness ratio of molded product For 20 particles that are cut approximately at the center cross section of the foamed particles within the cut surface of the molded product, the maximum inscribed circle of each particle cross section (radius R of the circle) Microscopic photographs of the inner and particle fused films were taken in the same manner as described above, the average thickness of the bubble film and the average thickness of the particle fused film were determined, and the ratio thereof was determined. Uniformity of bubbles Approximately 20 foam particle samples were cut at the center cross section and visually observed under 50x magnification.

[Table] Characteristics of the molded product (1) Degree of fusion 100 x 100 mm from the part of the molded product with a thickness of 20 mm or more
Cut out a square test piece, make a cut with a depth of 2 mm in the center, bend it along the cut, and split the molded product. The percentage of the number was calculated.

[Table] (2) Density Measured according to JIS K6767. (3) Dynamic buffer properties Measured according to JIS Z0234. The measurement conditions were a cushioning material thickness of 50 mm and a drop height of 60 cm, and the measured values are shown for the first drop. (4) Heating dimensional change A molded sample cut into a 200mm square shape was
Leave it at 25℃ for 24 hours, and place a 100 x 100 mm in the center.
Draw a square and a crosshair in the center, accurately measure the length of each segment, leave it for 96 hours in a constant temperature bath controlled at 100±1℃, take it out, leave it to cool at 25℃ for 1 hour, and measure the dimensions of the marked line. were measured, the rate of change (%) from the original dimensions was determined, and the average value was determined. Evaluation criteria: Less than 4%: No practical problem More than 4%: Not usable (5) Compression set Measured according to JIS K6767. Test conditions are 25
% constant compression. (6) Repeated compression set Measured according to JIS K6767. The test conditions are
It was set to 25% constant compression and repeated 80,000 times. (7) Sink Place a straight line ruler in the diagonal direction on the top surface of a molded plate-shaped test piece measuring 300 mm in length and width and 20 mm in thickness, find the maximum distance of the gap between the test piece and the ruler, and measure the length of the diagonal line. It was evaluated as a percentage of the

[Table] (8) Water absorption rate After cutting three test pieces of 50 x 50 x thickness from the molded product and accurately measuring their volume and weight,
After being immersed 25 mm below the surface of water at ℃ for 24 hours, the surface was quickly wiped off and the weight was accurately measured. The weight change before and after immersion is determined and calculated using the following formula. Water absorption rate (%) = Increase in weight (g) x 100/Volume of test piece (cc
)×density of water (g/cc) Evaluation was made using the average value of the obtained measurement results.

[Table] Example 1 Propylene ethylene random copolymer [ethylene component 6% by weight, random coefficient (R) 0.35, stereoregularity of propylene segment () 7.5%, 5
Kg/cm ² load Vikatsu softening point 48℃, melting point 135℃]
The material is extruded and shredded into granules, and volatile organic blowing agents (dichlorofluoromethane, dichlorofluoromethane,
BP-29.8°C) was added in a predetermined amount to the amount of resin to obtain expandable resin particles. When foaming these particles in a foaming pot at a foaming temperature of 135°C, the foamable resin particles are prepared in advance at a pressure below the equilibrium pressure of the foaming agent at the foaming temperature shown below.
Pressure atmosphere higher than the pressure at which foaming occurs (40-30Kg/cm ²
Gauge) for several tens of seconds, and then the pressure was released to a low pressure region where foaming occurs completely to cause foaming.

【table】

[Table] When the cross section of the expanded particles (hereinafter referred to as particles A) obtained under the conditions of Experiment No. 1 was observed with a microscope (×450),
A thick skin was formed on the surface, and the inside was composed of a large number of closed cells of relatively uniform small diameter (as shown in FIG. 1). Next, these foamed particles were heated at 90°C for 10
Inside the mold, pressurize with an air pressure of Kg/cm ² and adjust the internal pressure within the particle bubble to 2 Kg/cm ² to form a box shape with a cavity of 300 x 300 x 100 and a thickness of 20 mm. The molded product was heated with steam at 3.2 Kg/m ² (gauge pressure) to form a molded product, and after being removed from the mold, it was aged in a room at 90° C. for 8 hours. Various properties of the obtained molded bodies No. 11, 12, 13, and 14 were evaluated using the evaluation method described in the text, and the results are summarized in Table 1. A cross-sectional micrograph of compact No. 11 is shown in Fig. 3. Comparative Example 1 25% by weight volatile organic blowing agent in Example 1
The residence time below the equilibrium pressure of the foaming agent in the foaming pot was changed to 10 seconds and 5 seconds (Experiments No. 5 and 6) using the foamable resin particles containing the foaming agent (preferential volatilization of the foaming agent on the surface). Molded objects No. 15 and 16 obtained by repeating the experiment of Example 1 except that
The evaluation results are summarized in Table 1. A cross-sectional microscopic view (×450) of the expanded particles obtained in Experiment No. 5 (hereinafter referred to as particles B) is shown in FIG. 2, and that of the same molded product No. 15 is shown in FIG.

[Table] Table 1 shows that molded products in which the foam particle fusion film thickness is 8 times or more greater than the bubble film thickness inside the particles have excellent interparticle fusion degree, and the optimum stress in terms of dynamic buffer properties is on the high stress side. , it is clear that the maximum deceleration at that time is small and the maximum strain is small. In addition, dimensional changes due to heating are small and dimensional stability when exposed to high temperatures is excellent. The reason for this is that, as shown in Fig. 3, in a molded body using particles A with a thick skin thickness, a three-dimensional network-like fused part of the particles is formed in the molded body, resulting in mechanical deformation and This is thought to be because it exhibits a structural reinforcement effect against thermal deformation. Further, even when the expansion ratio is small, a molded product having a thick particle fusion portion exhibits excellent performance. Example 2, Comparative Example 2 Two experiments shown in (1) and (2) below were conducted for both the expanded particles (particles A) of Example 1 No. 1 and the expanded particles (particles B) of Comparative Example 1 No. 5. I went. (1) Store this indoors under natural conditions for 3 days and 7 days, respectively.
After leaving it for a day, it was heated with steam at 143°C for 5 seconds, kept in a room at 90°C for 15 hours, taken out, and left at 25°C for 24 hours to form expanded particles produced by the heat treatment. The expansion of the bulk volume of is expressed as a volume ratio. (2) Air is pressurized (impregnated) into each of the original expanded particle groups of both A and B, and the internal pressure of the particles is approximately 1.5 kg/
Adjust so that the pressure is cm ² (gauge pressure). The particles are then left indoors under natural conditions. (b) After being left for about 3 days, a portion of both foamed particles A and B are taken out, and the particles are subjected to in-mold molding as in Example 1 to obtain a molded article. (b) After being left to stand for about 7 days, the remaining foamed particles of both A and B are used to perform in-mold molding in the same manner as above to obtain a molded article. Evaluations of the results of these experiments (1), (2), (a), and (b) are summarized in Tables 2 and 3.

【table】

[Table] From Table 2, it can be seen that the expanded particles of the present invention last for a long period of time.
It is clear that the expansion ratio is kept high and the expansion ability is excellent. As shown in Table 3, this unique ability of expanded particles is also manifested when molded into molded products, resulting in excellent molded products with excellent fusion bonding, few sink marks, and low water absorption. As shown in Example 1, this is the cause of the excellent buffering performance. Example 3, Comparative Example 3 Each of the 15 types of propylene resin particles shown in Table 4-1 was placed in a pressure-resistant container, and a volatile organic blowing agent (dichlorodifluoromethane) was pressurized into the container. , the amount of foaming agent relative to the amount of resin
It is made into foamable resin particles containing 25% by weight. Each of the obtained foamable resin particles is heated and foamed in a foaming pot to each foaming temperature, and the atmospheric pressure is set to 40 to 35 kg/cm ² for post-foaming to form foamed particles with a thick skin. I tried my best to get it. At this time, for particles for which a skin cannot be obtained or for resin particles with a poor foaming state, the atmospheric pressure and residence time are varied, and the foamed particles judged to be the best are tested. The particles were then subjected to For each of the obtained expanded particles, the expansion ratio, skin film ratio, and bubble uniformity were evaluated by the method described in the text, and the results are shown in Table 4-2.

【table】

【table】

【table】

[Table] From Table 4-2, when the random coefficient (R) is larger than 0.7, the bubbles in the expanded particles become uneven;
It is clear that the thickness of the surface film is almost equal to the thickness of the bubble film, the random coefficient becomes larger, and foaming does not occur when the copolymer becomes a block copolymer. or,
Even if the random coefficient (R) is 0.7 or less, foaming will not occur if the stereoregularity () is 40% or more;
Even if it is less than 40%, if the softening point is higher than 50°C or lower than 35°C, it is clear that even if foaming occurs, the foaming efficiency will be low, the uniformity of the bubbles will be poor, and the surface film thickness will become thin. Example 4, Comparative Example 4 Expanded particles with experimental symbols No. A, C, C, and Wa shown in Table 4-2 were used, and the internal pressure of each particle was 1.0.
Kg/cm ² (gauge pressure) of air was injected (impregnated), and the particles were directly placed in the mold (Example 1).
(the same mold) was heated and foamed in the mold to obtain a molded product. In this case, water vapor of 2 kg/cm ² was used for preheating for about 15 seconds, followed by heating for forming at 3.2 kg/cm ² for 15 seconds, and then the product was cooled and taken out. The molded body taken out was aged in a room at 90°C for 8 hours. The various properties of the obtained molded bodies No. 21, 22, 23, and 24 were evaluated using the method described in the text, and the results were reported in the fifth section.
It is summarized in the table. Furthermore, the relationship between the maximum deceleration (G) and the static stress for compact No. 21 is shown in FIG. 5A, and the relationship with the instantaneous maximum strain is shown in FIG. 5B.

【table】

[Table] From Table 5, the foam of the present invention has dynamic cushioning properties,
It is clear that the foam has excellent compression properties and dimensional stability under heating. If a polymer other than the ethylene propylene random copolymer specified in the present invention is used, the skin thickness of the foamed particles will become small, resulting in poor foam molding performance during in-mold molding and a decrease in the degree of fusion. The resulting molded product has a high density, and only foams with inferior properties such as compression set, repeated compression set, and dimensional change upon heating can be obtained. Comparative Example 5 Various properties of a commercially available highly expanded polyolefin foam were evaluated by the method described in the text, and the results were
Shown in the table. The foam used was No. 31... Non-crosslinked polyethylene extruded foam (Asahi Dow, Esaform Q45) No. 32... Non-crosslinked polyethylene extruded foam (Asahi Dow, Esaform Q25) No. 33... ...It is a cross-linked polyethylene bead molded body (manufactured by Asahi Dow, MEF). Further, the relationship between the maximum deceleration (G) and the static stress is shown in Figure 5A, and the relationship with the maximum strain over the same time is shown in Figure 5B. As is clear from Table 5, the foam of the present invention is
Compared to commercially available highly expanded polyolefin foams of the same density, it has dynamic buffering properties with a higher optimum stress, lower maximum deceleration, and lower maximum strain, and has excellent performance as a packaging material. In particular, the small maximum strain means that bottoming out phenomenon is less likely to occur when packaged items with convex portions are cushioned, and exhibits excellent performance with a small amount of cushioning material, resulting in great economic effects. In addition, the small dimensional change due to heating indicates that the material is a highly reliable cushioning material, as it does not cause the cargo to collapse due to the temperature increase in the hold during export, nor does it suffer from deterioration in cushioning performance due to the cushioning material becoming stale. Furthermore, it has the advantage that it can be used in a high temperature atmosphere, which is not possible with conventional foams. From FIG. 5, it is clear that the foam of the present invention has an optimal buffering stress on the high stress side and a smaller maximum strain than the polyethylene foam with the same density, and the polyethylene foam has almost the same optimal stress. It is clear that the instantaneous maximum strain is small compared to the foam body, and it has excellent performance and is economical because the density of the foam can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional microscopic photograph of foamed particles with a thick skin film according to the present invention, FIG. 2 is a cross-sectional microscopic photograph of foamed particles with a thin skin film for comparison, and FIG. 3 is the same as that shown in FIG. FIG. 4 is a cross-sectional micrograph showing the particle fused film of a molded product obtained from expanded particles, and FIG. 4 is a cross-sectional micrograph showing a particle fused film of a molded product obtained from expanded particles shown in FIG. Photographic diagram, Figure 5 A,
B is a diagram showing the dynamic cushioning properties (A impact properties, B instantaneous maximum strain) of the molded article of the present invention (Curve 1) and the commercially available highly foamed polyethylene foam (Curves 2 to 4).

Claims (1)

[Scope of Claims] 1. A foamed molded article constituted by a large number of propylene resin foam particles having a fine cell structure, the surfaces of which are in contact with each other and fused and aggregated: (a) a propylene resin; is a propylene-ethylene random copolymer having a propylene component of 90% by weight or more and an ethylene component of 10% by weight or less,
Random coefficient (R) is 0.7 or less, stereoregularity of propylene segment () is less than 40%, 5Kg
The copolymer has a softening point under load of approximately 50 to 35°C, (b) the resin foam is substantially non-crosslinked, and (c) the resin foam formed by the above fusion aggregation 1. A foam molded article made of polypropylene resin foam particles, characterized in that the fused film is about 8 times or more thicker than the cell membrane inside the particles. 2 A propylene-ethylene random copolymer containing 90% by weight or more of propylene component and 10% by weight or less of ethylene component, with a random coefficient (R) of 0.7
Below, stereoregularity of propylene segment ()
is less than 40%, and the Vikatsu softening point at a load of 5Kg/ ^cm2 is approximately
The copolymer has a boiling point of -50 to 35℃.
A volatile organic blowing agent at 110°C is contained to form foamable resin particles, and then the foaming agent present on the surface of the foamable resin particles is preferentially volatilized, and then the entire particles are foamed. A molded product obtained by forming foamed particles with a thick skin, then imparting foaming ability to the foamed particles, and heating and foaming them in a mold in a non-crosslinked state to fuse the surfaces of the particles to each other and integrate them. A molded article made of foamed propylene resin particles, characterized in that the fused film produced by the fusion is about 8 times or more larger than the cell membrane constituting the particles inside the molded article. manufacturing method.